As the pin-up girl of the Restoration, Nell Gwyn seems to have constantly fallen prey to wardrobe malfunctions. Simon Verelst's two portraits of her show her first experiencing what paparazzi refer to as "nipple slip", and then to have lost control of her bodice entirely (it is this kind of page 3 version of the actress that Samuel Pepys, and many of his peers, kept as a pocket reminder of the king's favourite). The energy of Verelst's portraits – show-stoppers in the National Portrait Gallery's The First Actresses – lies not so much in the disorganised décolletage of the actress, however, but in the consummate coolness of her gaze. It's both shameless and knowing, this look; the screw-you stare of the authentic star.

"Pretty witty Nell", as Pepys called her, was the first recognisable celeb in British popular culture; post-Puritan politics had created a gap in the market for a certain kind of sexual frankness, and Gwyn effortlessly filled it: the sensational shock of her immodesty retains its centuries-old power.

Gwyn was, it seems, also a very hard actress to follow. The headline acts who assumed her mantle – Hester Booth in a harlequin frock; Lavinia Fenton, who like Gwyn rose from teenage barmaid to leading lady; the great comedienne Kitty Clive – borrow a lot of her look in their portraits but do not quite live up to her outrageousness. (It's a bit like seeing Andy Warhol's silkscreen of Farrah Fawcett after his Marilyn series.)

If Gwyn set a Monroe-ish standard for star quality, she also appears to have established a precedent for promiscuity; Fenton, who excited male audiences in her cross-dressing "breeches" roles, is pictured by Hogarth being leered at by Charles Powlett, the Duke of Bolton, as she takes the role of Polly in The Beggar's Opera. Fenton retired from the stage at 20 – already praised by Alexander Pope as "the great favourite of the town; her pictures engraved and sold in great numbers, her life written, books of letters and verses to her published" – to become the duke's mistress, and mother to his three sons.

Other actresses became the subject of gossip about involvement with their fellow performers; Peg Woffington, also invariably portrayed nearly spilling out of her frock, became the lover of David Garrick after playing Cordelia to his Lear in 1741. (Garrick, whose life runs in parallel with many of the subjects of this exhibition, is pictured in later years with his wife Eva-Maria in a florid portrait by Joshua Reynolds; he appears to be awaiting applause after declaiming a passage from Shakespeare; she appears to have heard it all before.)

Even as actresses became more "respectable", the associations with easy virtue persisted; Covent Garden and Drury Lane were as infamous for their prostitutes as their stage-stars, and the perception that the two trades were intimately linked proved hard to shift. It is not until Sarah Siddons directs her full attention to the viewer in Sir Thomas Lawrence's portrait of 1804 that an actress seems at liberty to be anything other than a subject of desire. Siddons, a close friend of Samuel Johnson, and famed for her Lady Macbeth, elevated her profession almost single-handedly by all accounts; you can see a lot of that moral rigour in Lawrence's painting: she is dressed in black velvet, leafing through a vast book, and her look is no longer one of coy suggestibility but serious intent. Nearly a century and a half after women had been allowed back on stage, the leading lady had apparently arrived.

The story of the National Portrait Gallery's exhibition is set in motion by the return of Charles II from exile in the Hague in 1660 and his re-establishment of the theatres. The Netherlands of those years was not, you imagine, a place that could have accommodated Nell Gwyn in its popular culture; no doubt, for the king, that was part of the attraction.

There is something far more austerely Cromwellian about the ideals of female beauty in Vermeer's Women at the Fitzwilliam in Cambridge. It is, nonetheless, a dazzling spectacle. Whereas the portrait gallery's actresses seem all about availability to the male gaze, the women who inhabit these Dutch interiors – by Vermeer and his contemporaries – retain a profound mystery and reserve. Just occasionally the artist seems to have chanced upon an unwarranted intimacy: in Jan Steen's Woman at Her Toilet the figure is unrolling her red stocking on the edge of her bed, but she seems unaware of the viewer's presence, entirely absorbed in her mundanely sensual task. This feminine self-absorption is the quality that these painters most prized, and no one was more capable of realising it than Vermeer. His small masterpiece, The Lacemaker, is on loan from the Louvre and is worth the journey to Cambridge itself, as an unequalled study in needle-sharp attention, both of artist and sitter.

The more you look at these three rooms of paintings, nearly all made in the 15 years between 1655 and 1670, the more curious you become about the detailed world that created them. The Dutch of the period promoted domestic goddesses of a certain kind in household manuals called things like: On the Excellence of the Female Sex. On one level the paintings of Vermeer, Samuel van Hoogstraten, Pieter de Hooch and Gerard ter Borch seem to be propagandising just this kind of female virtue that is anything but easy – the responsibility and grind of wife and mother. Heads bent in concentration, the women attend to their sewing or – if of a more elevated social position – their musical study at the virginal. They mind children in cots, they examine fish for supper. The more you look, though, the more you sense that behind this depiction of domestic ritual is always a kind of wonder. Vermeer's paintings in particular, nearly all made in the front room of the house in Delft he shared with his mother-in-law and wife and 10 children, seem the most intense expression of the unknowable quality of other lives; for all their impossible mastery of light and lustre, they stop just deliberately short of any attempt at understanding, giving his women an ineffable existence all of their own.

There are many other little marvels here – van Hoogstraten's highly charged but uninhabited View of an Interior, in which we are granted visual access through three doors, the last of them just unlocked, keys dangling, to reveal only a discarded pair of slippers at the threshold of an immaculately swept floor, an everyday holy of holies; or de Hooch's everything-is-illuminated Courtyard of a House in Delft which makes your eyes quickstep continually from one perfectly realised piece of brickwork to the next. But it is the extreme stillness of Vermeer's women you want to return to; actresses who are always anything but.